Method for manufacturing secondary battery

Abstract

To provide a secondary battery which improves safety by guiding to exhaust gas in a specific direction.SOLUTION: A secondary battery includes: an electrode assembly on which an electrode lead is mounted; a case including a storage part for storing the electrode assembly, and a sealing part which contains a sealant resin and is formed so as to seal the electrode assembly; a lead film which covers and wraps a part of the outer surface of the electrode lead, and is interposed between the electrode lead and the case; a vent area formed in at least a part of the case; and a vent member which includes a first layer containing a resin having a melting point lower than that of the sealant resin, and a second layer which is positioned on at least one surface of the first layer and contains an adhesive substance, and is inserted into the vent area, wherein the thickness of the second layer is 5 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and more particularly to a secondary battery provided with a vent member.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0001217, filed on January 4, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] Secondary batteries, which have high applicability across product groups and electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are powered by electrical sources. These batteries are attracting attention as a new energy source for improving energy efficiency, as they are environmentally friendly because they do not produce any by-products from energy use, in addition to their primary advantage of dramatically reducing the use of fossil fuels.

[0004] Currently widely used secondary batteries include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel metal hydride batteries, and nickel zinc batteries.

[0005] Such secondary batteries are generally constructed in such a way that an electrode assembly including at least one unit cell having a positive electrode / separator / negative electrode structure is housed in a case, and the electrode assembly is sealed by fusing a sealant resin inside the case.

[0006] In such conventional secondary batteries, fires can occur due to various causes, such as short circuits inside the secondary battery, overcharging or over-discharging, temperature control, etc. When this happens, the internal temperature of the secondary battery rises rapidly, and at the same time, thermal propagation occurs, in which heat is transferred to adjacent cells, which can cause the fire to spread further.

[0007] To minimize damage to electrodes caused by gas when thermal runaway occurs, secondary batteries require directional venting, which allows gas to be released in one direction when the internal temperature of the battery rises. However, conventional secondary batteries have difficulty in guiding gas release in a specific direction. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a secondary battery that can guide gas discharge in a specific direction, thereby improving safety. [Means for solving the problem]

[0009] In order to achieve the above object, according to one aspect of the present invention, there is provided a secondary battery of the following embodiment.

[0010] The first embodiment is an electrode assembly having an electrode lead attached thereto; a case including a receiving portion for receiving the electrode assembly and a sealing portion including a sealant resin and formed to seal the electrode assembly; a lead film that covers a part of an outer surface of the electrode lead and is interposed between the electrode lead and the case; a vent area formed in at least a portion of the case; a vent member that includes a first layer containing a resin having a melting point lower than that of the sealant resin, and a second layer that is positioned on at least one surface of the first layer and contains an adhesive material, and is inserted into the vent area; The present invention relates to a secondary battery characterized in that the thickness of the second layer is 5 μm or less.

[0011] According to the second embodiment, in the first embodiment, The vent area may be located in the sealing portion.

[0012] According to the third embodiment, in the second embodiment, The vent member may be formed longer than the sealing portion, and the vent member may be exposed to both the inside and outside of the case.

[0013] According to the fourth embodiment, in the third embodiment, The second layer may be located on at least one side of the first layer exposed to the outside of the case.

[0014] According to the fifth embodiment, in any one of the first to fourth embodiments, The resin having a lower melting point than the sealant resin may include linear low density polyethylene having a comonomer having six or more carbon atoms.

[0015] According to the sixth embodiment, in the fifth embodiment, The resin having a melting point lower than that of the sealant resin may include linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0016] According to the seventh embodiment, in the fifth or sixth embodiment, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst.

[0017] According to the eighth embodiment, in any one of the fifth to seventh embodiments, In the linear low-density polyethylene having a comonomer having 6 or more carbon atoms, the content of the comonomer having 6 or more carbon atoms may be 15% by weight or less, based on 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

[0018] According to the ninth embodiment, in any one of the fifth to eighth embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a polydispersity index (PDI) of 4 or less.

[0019] According to the tenth embodiment, in any one of the fifth to ninth embodiments, The difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 10°C or less.

[0020] According to the eleventh embodiment, in any one of the fifth to tenth embodiments, The crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 90°C to 115°C.

[0021] According to the twelfth embodiment, in any one of the fifth to eleventh embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a weight average molecular weight of 100,000 g / mol to 400,000 g / mol.

[0022] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, The vent member can perform venting at 100°C to 120°C.

[0023] According to the 14th embodiment, in any one of the 1st to 13th embodiments, The vent member is capable of venting at a pressure of 1.5 atm or greater.

[0024] According to the fifteenth embodiment, in any one of the first to fourteenth embodiments, The vent member may have a maximum sealing strength of less than 6 kgf / 15 mm at 100° C. or higher.

[0025] According to the 16th embodiment, in any one of the 1st to 15th embodiments, The vent member may have an average sealing strength of less than 4.5 kgf / 15 mm at 100° C. or higher.

[0026] According to the seventeenth embodiment, in any one of the first to sixteenth embodiments, The vent member may have a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C.

[0027] According to the 18th embodiment, in any one of the 1st to 17th embodiments, The vent member may have an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C.

[0028] According to the 19th embodiment, in any one of the 1st to 18th embodiments, The resin having a melting point lower than that of the sealant resin may have a melting point of 100°C to 130°C.

[0029] According to the 20th embodiment, in any one of the 1st to 19th embodiments, The adhesive material may include an acrylic polymer, a polyurethane, an epoxy resin, a silicone, a butyl rubber, a polyisobutylene, or two or more of these.

[0030] According to the 21st embodiment, in any one of the 1st to 20th embodiments, The vent area may be located in a sealing portion at a corner side of the case.

[0031] According to the 22nd embodiment, in any one of the 1st to 21st embodiments, The secondary battery may be a pouch-type secondary battery. [Effects of the Invention]

[0032] The secondary battery according to an embodiment of the present invention includes a vent member including a resin having a lower melting point than the sealant resin of the case, thereby guiding gas discharge in the direction of the vent member, thereby improving the safety of the battery.

[0033] In a secondary battery according to an embodiment of the present invention, a second layer including an adhesive material is disposed on at least one surface of a first layer, thereby fixing the position of a vent member and improving the dimensional stability of the battery.

[0034] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concepts of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in the drawings. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 10 is a diagram showing a secondary battery in which the vent member does not include a layer containing an adhesive material. [Figure 2] 1 is a view showing a secondary battery according to an embodiment of the present invention, in which a vent member includes a layer containing an adhesive material; [Figure 3] FIG. 2 is an enlarged view of a vent member according to an embodiment of the present invention. [Figure 4] FIG. 10 is a diagram illustrating a secondary battery according to another embodiment of the present invention. [Figure 5] 5 is a partially enlarged cross-sectional view of the vent member after the sealing portion of the secondary battery of FIG. 4 has been sealed. [Figure 6] 10 is a partially enlarged view of a vent member in a secondary battery according to still another embodiment of the present invention; FIG. [Figure 7] 10 is a partially enlarged view of a vent member in a secondary battery according to still another embodiment of the present invention; FIG. [Figure 8] 10 is a partially enlarged view of a vent member in a secondary battery according to still another embodiment of the present invention; FIG. [Figure 9] FIG. 3 is a cross-sectional view taken along line BB' in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0036] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in the specification and claims should not be construed as being limited to their ordinary and dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventors themselves can appropriately define the concepts of terms in order to best describe the invention.

[0037] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of the present invention, and that there may be various equivalents and modifications that can be substituted therefor at the time of this application.

[0038] According to one aspect of the present invention, there is provided a secondary battery comprising: an electrode assembly having an electrode lead attached thereto; a case including a housing for housing the electrode assembly and a sealing portion formed to seal the electrode assembly, the sealing portion including a sealant resin; a lead film that covers a portion of an outer surface of the electrode lead and is interposed between the electrode lead and the case; a vent region formed in at least a portion of the case; and a vent member inserted into the vent region, the vent member including: a first layer including a resin having a lower melting point than the sealant resin; and a second layer positioned on at least one surface of the first layer and including an adhesive material, wherein the second layer has a thickness of 5 μm or less.

[0039] FIG. 1 shows a secondary battery in which the vent member does not include a layer containing an adhesive material. The secondary battery 10 includes an electrode assembly 12 to which an electrode lead 11 is attached, and a case 13. The case 13 includes a housing portion 13a for housing the electrode assembly 12 and a sealing portion 13b for sealing the electrode assembly 12. The secondary battery 10 also includes a lead film 14. The lead film 14 covers a portion of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the sealing portion 13b. The lead film 14 is interposed between the electrode lead 11 and the sealing portion 13b to assist in bonding the electrode lead 11 to the sealing portion 13b.

[0040] 1, if the vent member 15 for guiding gas discharge in a specific direction does not include a layer containing an adhesive material, the vent member 15 is simply inserted into the case 13 and then the battery is sealed. However, if the vent member 15 is simply inserted into the case 13, the vent member 15 is not fixed until the case 13 is sealed, which causes a problem of reduced dimensional stability.

[0041] The inventors discovered that by placing a layer containing an adhesive substance on at least one surface of the vent member, the vent member can be accurately fixed and dimensional stability can be ensured even before the case is sealed, which led to the completion of the present invention.

[0042] FIG. 2 is a diagram illustrating a secondary battery according to an embodiment of the present invention, in which a vent member includes a layer containing an adhesive material.

[0043] Referring to FIG. 2, a secondary battery 10 according to an embodiment of the present invention includes an electrode assembly 12 to which an electrode lead 11 is attached, and a case 13.

[0044] The electrode assembly 12 includes a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly 12 may include a positive electrode plate and a negative electrode plate stacked in order with a separator interposed therebetween.

[0045] The positive electrode plate may include a positive electrode current collector made of a highly conductive metal sheet, such as aluminum (Al) foil, and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode plate may also include a positive electrode tab made of a metal material, such as aluminum (Al), at one end. The positive electrode tab may extend and protrude from one end of the positive electrode plate, or may be attached to one end of the positive electrode plate using welding or a conductive adhesive.

[0046] The negative electrode plate may include a negative electrode current collector made of a conductive metal thin plate, for example, copper (Cu) foil, and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode plate may also include a negative electrode tab at one end made of a metal material, for example, copper (Cu) or nickel (Ni). The negative electrode tab may extend and protrude from one end of the negative electrode plate, or may be attached to one end of the negative electrode plate using welding or a conductive adhesive.

[0047] The separator may be formed in the form of a porous membrane that is interposed between the positive and negative electrode plates to electrically insulate them and allow lithium ions to pass between the positive and negative electrode plates. Such a separator may include, for example, a porous membrane using polyethylene (PE), polypropylene (PP), or a composite film thereof.

[0048] The surface of the separator may be provided with an inorganic coating layer, which may have a structure in which inorganic particles are bound to each other by a binder to form a pore structure (interstitial volume) between the particles.

[0049] Examples of the electrode assembly 12 include a jelly roll (wound) electrode assembly in which long sheet-like positive and negative electrodes are wound with a separator interposed therebetween, a stacked electrode assembly in which a plurality of positive and negative electrodes cut into units of a predetermined size are stacked in sequence with a separator interposed therebetween, and a stacked / folded electrode assembly in which a bi-cell or full-cell in which a predetermined unit of positive and negative electrodes is stacked with a separator interposed therebetween is wound up.

[0050] Referring to FIG. 2, the case 13 includes a receiving portion 13a for receiving the electrode assembly 12 and a sealing portion 13b for sealing the electrode assembly 12.

[0051] The sealing portion 13b includes a sealant resin, and the sealant resin is fused along the outer circumferential surface of the receiving portion 13a to seal the electrode assembly 12.

[0052] In one embodiment of the present invention, the case 13 may be provided in the form of a multi-layered film including an outer layer for protection from external impact, a metal barrier layer for blocking moisture, and a sealant layer for sealing the case.

[0053] The outer layer may include polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, nylon, or other polyester-based films, and may be constructed as a single layer or multiple layers.

[0054] The metal barrier layer may include aluminum, copper, and the like.

[0055] The sealant layer may include a sealant resin and may be composed of a single layer or multiple layers.

[0056] The sealant resin may include polypropylene (PP), acid-modified polypropylene (PPa), random polypropylene, ethylene-propylene copolymer, or two or more thereof. The ethylene-propylene copolymer may include, but is not limited to, ethylene-propylene rubber, ethylene-propylene block copolymer, etc.

[0057] In one embodiment of the present invention, the case 13 may be a pouch type.

[0058] In one embodiment of the present invention, when the case 13 is a pouch type, it may include an upper pouch and a lower pouch. When the case 13 includes an upper pouch and a lower pouch, the upper pouch and the lower pouch may be arranged so that the sealant resins face each other, and then the facing sealant resins may be fused together by heat and pressure to seal the battery.

[0059] The sealing portion 13b may be fused by heat or ultrasonic waves, but is not particularly limited as long as the sealing portion 13b can be fused.

[0060] The sealing portion 13b may be four-sided sealed or three-sided sealed around the periphery of the case 13. The three-sided sealed structure refers to a structure in which an upper pouch and a lower pouch are formed from a single pouch sheet, and then the boundary between the upper pouch and the lower pouch is folded to overlap the housing portions 13a of the electrode assemblies formed in the upper pouch and the lower pouch, and the remaining three peripheries excluding the folded portion are sealed.

[0061] Referring to FIG. 2, the electrode lead 11 may be housed in the battery case 13 such that a portion of the electrode lead 11 is exposed to the outside of the battery case 13 .

[0062] Referring to FIG. 2, a secondary battery 10 according to one embodiment of the present invention includes a lead film 14 .

[0063] The lead film 14 covers a portion of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the sealing portion 13b. The lead film 14 is interposed between the electrode lead 11 and the sealing portion 13b to assist in bonding the electrode lead 11 and the sealing portion 13b.

[0064] 2, a secondary battery 10 according to an embodiment of the present invention includes a vent region (not shown) formed in at least a portion of the case 13, and a vent member 15 can be inserted into the vent region. The vent member 15 can improve the safety of the battery by guiding gas discharge in a specific direction when a thermal runaway phenomenon occurs.

[0065] In one embodiment of the present invention, the vent area may be located in the sealing portion 13b.

[0066] In one embodiment of the present invention, the vent region may be located in the sealing portion excluding the sealing portion on the side where the electrode lead 11 is exposed to the outside.

[0067] In another embodiment of the present invention, the vent area may be located in the sealing portion on the side where the electrode lead 11 is exposed to the outside.

[0068] In yet another embodiment of the present invention, the vent area may be located at a corner sealing portion of the case 13. When the vent area is located at a corner sealing portion of the case 13, the amount of gas vented in a direction that directly contacts the electrode lead 11, i.e., toward the side of the electrode lead 11, can be minimized, further improving the safety of the battery.

[0069] FIG. 3 is an enlarged view of a vent member according to one embodiment of the present invention.

[0070] Referring to FIG. 3, the vent member 15 includes a first layer 15a containing a resin having a melting point lower than that of the sealant resin, and a second layer 15b located on at least one surface of the first layer 15a and containing an adhesive material.

[0071] The vent member 15 includes a resin with a lower melting point than the sealant resin of the sealing portion 13b, so that the sealing strength of the portion where the vent member 15 is inserted is lower than the sealing strength of the portion of the sealant resin where the vent member 15 is not inserted at high temperatures, thereby making it easier to implement venting characteristics. As a result, when a thermal runaway phenomenon occurs, gas can be discharged in a specific direction, improving the safety of the battery.

[0072] In addition, the vent member 15 includes a second layer 15b containing an adhesive material on at least one surface of a first layer 15a containing a resin with a lower melting point than the sealant resin, which makes it easier to fix the position of the vent member 15. That is, it is possible to reduce positional deviation of the vent member 15. For example, the positional deviation of the vent member 15 can be within 0.5 mm.

[0073] In one embodiment of the present invention, at least a portion of the vent member 15 may be located in the sealing portion 13b.

[0074] In another embodiment of the present invention, at least a portion of the vent member 15 may be exposed to the outside of the case 13 .

[0075] FIG. 4 is a diagram showing a secondary battery according to another embodiment of the present invention.

[0076] 4, the vent member 15 may be formed longer than the sealing portion 13b, and the vent member 15 may be exposed to both the inside and outside of the case 13. That is, one end of the vent member 15 may be located closer to the battery inner side than the battery inner end of the sealing portion 13b, and the other end of the vent member 15 may be located closer to the battery outer side than the battery outer end of the sealing portion 13b. When the vent member 15 has such a structure, the vent effect can be further improved.

[0077] 5 is a partially enlarged cross-sectional view of the vent member after the sealing portion of the secondary battery of FIG. 4 has been sealed.

[0078] 5, when a portion of the vent member 15 is exposed to the outside of the case 13, the second layer 15b may be located on at least one surface of the first layer 15a exposed to the outside of the case 13. During the process of inserting the vent member including the second layer 15b into the case 13 and then sealing it, the second layer 15b may be pushed out of the case 13. As a result, the second layer 15b may not be present inside the case 13 but may be present only on the outside of the case 13. That is, the second layer 15b may be located only on at least one surface of the first layer 15a exposed to the outside of the case 13. While the adhesive material of the second layer 15b accurately fixes the vent member 15 in a desired position, when the sealing portion 13b and the first layer 15a overlap, the adhesive material may actually hinder the overlapping of the sealing portion 13b and the first layer 15a, which may reduce the sealing strength between the sealing portion 13b and the first layer 15a. When the second layer 15b is located on at least one side of the first layer 15a exposed to the outside of the case 13, the problem of a decrease in the sealing strength between the sealing portion 13b and the first layer 15a can be more easily prevented.

[0079] The vent member 15 and the case 13 may be overlapped by heat sealing. As another example, the vent member 15 and the case 13 may be overlapped by an adhesive such as glue. As yet another example, the vent member 15 and the case 13 may be physically connected by a clip or the like. As yet another example, at least a portion of the vent member 15 may be embedded in a film that constitutes the case 13, for example, a sealant resin.

[0080] In the present invention, the thickness of the second layer 15b is 5 μm or less. For example, the thickness of the second layer 15b may be 100 nm to 5 μm or 1 to 5 μm. When the thickness of the second layer 15b satisfies the above range, the battery is sealed during normal operation and gas can be released only during abnormal operation of the battery.

[0081] If the thickness of the second layer 15b exceeds 5 μm, the second layer 15b containing the adhesive becomes too thick when the sealing portion 13b and the first layer 15a overlap, reducing the sealing strength between the sealing portion 13b and the first layer 15a. This makes it difficult to ensure the desired sealing strength during normal battery operation. For example, the maximum sealing strength during normal battery operation may be 6 kgf / 15 mm or less.

[0082] In one embodiment of the present invention, the resin having a lower melting point than the sealant resin may include linear low-density polyethylene having a comonomer with 6 or more carbon atoms. By including linear low-density polyethylene having a comonomer with 6 or more carbon atoms as the resin having a lower melting point than the sealant resin, the case 13 has excellent sealing properties, and the sealing strength of the case 13 with the vent member 15 inserted therein decreases at high temperatures, making it possible to easily realize venting characteristics.

[0083] In one embodiment of the present invention, the resin having a melting point lower than that of the sealant resin may include linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0084] In one embodiment of the present invention, the resin having a lower melting point than the sealant resin may have a melting point of 100°C to 130°C, 105°C to 125°C, or 110°C to 120°C. When the resin having a lower melting point than the sealant resin includes a linear low-density polyethylene having a comonomer with six or more carbon atoms, the linear low-density polyethylene having a comonomer with six or more carbon atoms may have a melting point of 100°C to 130°C, 105°C to 125°C, or 110°C to 120°C. When the resin having a lower melting point than the sealant resin has a melting point within the above range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100°C, making it easier to achieve venting characteristics.

[0085] The melting point of a resin having a lower melting point than the sealant resin can be measured using a differential scanning calorimeter (DSC). For example, the temperature of a sample is increased from 30°C to 280°C at 10°C / min, maintained at 280°C for 10 minutes, cooled to 30°C at 10°C / min, and maintained at 30°C for 10 minutes. The melting point can then be measured by increasing the temperature from 30°C to 280°C at 10°C / min, and maintaining the temperature at 280°C for 10 minutes.

[0086] In one embodiment of the present invention, the vent member 15 can perform venting at 100°C to 120°C.

[0087] In one embodiment of the present invention, the vent member 15 is capable of venting at a pressure of 1.5 atm or more.

[0088] In one embodiment of the present invention, the vent member 15 can perform venting at 100° C. to 120° C. and a pressure of 1.5 atm or more.

[0089] The vent member 15 vents within the above temperature range and / or pressure conditions, so that the battery can be sealed during normal battery operation, and gas can be more easily released only during abnormal battery operation.

[0090] In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm at temperatures above 100° C. If the vent member 15 satisfies the above-mentioned sealing strength within the above-mentioned temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100° C., and the venting characteristics can be easily realized.

[0091] In addition, in one embodiment of the present invention, the maximum sealing strength of the vent member 15 may be 6 kgf / 15 mm or more at room temperature to 60° C. If the vent member 15 satisfies the above-mentioned sealing strength within the above-mentioned temperature range, even when the vent member 15 is inserted, the vent member 15 has excellent sealing strength during normal battery operation, and the hermeticity of the battery can be easily ensured.

[0092] In one embodiment of the present invention, the maximum sealing strength of the vent member 15 at temperatures of 100°C or higher may be less than 6 kgf / 15 mm, and the maximum sealing strength of the vent member 15 at room temperature to 60°C may be 6 kgf / 15 mm or higher. When the vent member 15 satisfies the above-mentioned sealing strength, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, making it easy to realize vent characteristics, and during normal battery operation, the vent member 15 has excellent sealing strength, making it easy to ensure the hermeticity of the battery.

[0093] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm at temperatures above 100° C. If the vent member 15 satisfies the above-mentioned sealing strength within the above-mentioned temperature range, the sealing strength of the portion of the case 13 where the vent member 15 is inserted decreases at high temperatures, making it easier to implement venting characteristics.

[0094] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60° C. If the vent member 15 satisfies the above-mentioned sealing strength in the above-mentioned temperature range, it has excellent sealing strength during normal operation of the battery, and can easily ensure the hermeticity of the battery.

[0095] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm at temperatures above 100° C. and an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60° C. When the vent member 15 has a temperature range as described above, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, making it easy to realize vent characteristics, and the vent member 15 has excellent sealing strength during normal battery operation, making it easy to ensure the hermeticity of the battery.

[0096] The sealing strength of the vent member 15 according to temperature can be measured by cutting the part of the case 13 where the vent member 15 is inserted to a width of 15 mm and a length of 5 cm, opening both ends 180°, fixing them to a UTM jig, and conducting a tensile test at a speed of 5 mm / min.

[0097] Here, the maximum sealing strength refers to the maximum value at which the case 13 breaks. In addition, the average sealing strength refers to the average value when the case 13 is stretched by 8 mm under the condition of 4.5 kgf / 15 mm or more when the maximum sealing strength is 4.5 kgf / 15 mm or more, and refers to the average value when the case 13 is stretched by 8 mm under the maximum sealing strength when the maximum sealing strength is less than 4.5 kgf / 15 mm.

[0098] In one embodiment of the present invention, the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst. When the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is polymerized in the presence of a metallocene catalyst, it has more advantageous sealing strength and physical properties than when polymerized in the presence of a Ziegler-Natta catalyst.

[0099] In one embodiment of the present invention, the content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 15 wt% or less, 12 wt% or less, 11.8 wt% or less, 10 wt% or less, 9 wt% or less, 8 wt% or less, or 7.6 wt% or less, based on 100 wt% of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. The content of the comonomer having 6 or more carbon atoms may be 5 wt% or more, 7.6 wt% or more, 8 wt% or more, 9.0 wt% or more, 10 wt% or more, 11.8 wt% or more, or 12 wt% or more, based on 100 wt% of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. When the content of the comonomer having 6 or more carbon atoms is within the above range, it is possible to easily prevent a decrease in intermolecular packing density, which would otherwise result in a decrease in sealing strength during normal battery operation.

[0100] The content of the comonomer having 6 or more carbon atoms can be measured by H-NMR. For example, about 10 mg of a sample is completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, and then sampled into an NMR tube. 1 It can be measured using H-NMR.

[0101] In one embodiment of the present invention, the weight-average molecular weight of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 100,000 g / mol to 400,000 g / mol, 200,000 g / mol to 350,000 g / mol, or 230,000 g / mol to 300,000 g / mol. When the weight-average molecular weight of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms satisfies the above range, the sealing strength during normal operation of the battery can be further improved.

[0102] In one embodiment of the present invention, the polydispersity index (PDI) of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 4 or less, 3.8 or less, 3.796 or less, 3.5 or less, 3.023 or less, 3 or less, 2.7 or less, or 2.674 or less. The polydispersity index (PDI) may be 1.0 or more. When the polydispersity index of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms satisfies the above range, the molecular weight distribution is narrow, and thus the battery exhibits better sealing strength and physical properties during normal operation.

[0103] The weight average molecular weight and polydispersity index of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be measured by gel permeation chromatography (GPC) under the following conditions.

[0104] -Column: Tosoh HLC-8321 GPC / HT Solvent: TCB (trichlorobenzene) + 0.04% BHT (dried with 0.1% CaCl2) -Flow rate: 1.0ml / min -Sample concentration: 1.5mg / ml -Injection volume: 300μl -Column temperature: 160℃ -Detector: RI detector -Standard: Polystyrene (corrected by a cubic function)

[0105] In one embodiment of the present invention, the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be similar. For example, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 10°C or less, or 5°C or less. Furthermore, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 0.1°C or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms satisfies the above-mentioned range, the fusion properties between the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms during normal operation of the battery are more excellent.

[0106] In one embodiment of the present invention, the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 90°C to 115°C, 95°C to 110°C, 100°C to 110°C, or 105°C to 110°C. When the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms satisfies the above-mentioned range, the fusion properties between the sealant resin and the linear low-density polyethylene having a comonomer having 6 or more carbon atoms become more excellent.

[0107] The crystallization temperature can be measured using a differential scanning calorimeter (DSC). For example, the temperature of a sample can be increased from 30°C to 280°C at 10°C / min, maintained at 280°C for 10 minutes, cooled to 30°C at 10°C / min, and maintained at 30°C for 10 minutes. The crystallization temperature can then be measured by increasing the temperature from 30°C to 280°C at 10°C / min, and maintaining the temperature at 280°C for 10 minutes.

[0108] In one embodiment of the present invention, the vent member 15 may have a film shape.

[0109] The vent member 15 may be formed to have a predetermined thickness. Furthermore, the vent member 15 may be inserted into the case 13 to vary the insertion length or to control the venting pressure and position depending on the design.

[0110] In one embodiment of the present invention, the insertion length of the vent member 15 may be 5 to 20 mm.

[0111] In one embodiment of the present invention, when the sealing portion 13b is sealed on three sides, the bent surface of the case and one end of the vent member 15 may be adjacent to each other.

[0112] In one embodiment of the present invention, the vent member 15 may have a shape that narrows toward the outside of the case 13. When the vent member 15 has a shape that narrows toward the outside of the case, the spray angle of the vented gas is reduced, thereby further improving the safety of the battery. In particular, when the vent member 15 is located in the sealing portion on the side where the electrode lead 11 is exposed to the outside or in the sealing portion on the corner side of the case, the amount of gas vented toward the side of the electrode lead 11 can be minimized, thereby further improving the safety of the battery.

[0113] 6 to 8 are partially enlarged views of a vent member in a secondary battery according to still another embodiment of the present invention.

[0114] 6 and 7, the shape of the vent member 15 may be, for example, elliptical or stepped, but the shape of the vent member 15 may be modified to a circular, triangular, trapezoidal, or the like.

[0115] 8, the vent member 15 may have an asymmetrical stepped shape. When the vent member 15 is located in the sealing portion on the side where the electrode lead 11 is exposed to the outside or in the sealing portion on the corner side of the case, the step of the step may be formed to correspond to the side of the electrode lead 11. In this case, the ejection direction of the vented gas can be separated from the side of the electrode lead 11 as far as possible.

[0116] In one embodiment of the present invention, the thickness of the vent member 15 may decrease continuously or discontinuously along the direction in which the electrode lead 11 protrudes.

[0117] FIG. 9 is a cross-sectional view taken along the line BB' in FIG.

[0118] Referring to FIG. 9, the thickness of the vent member 15 may decrease discontinuously in a stepwise manner as shown in FIG. 9(a), or may decrease continuously as shown in FIG. 9(b).

[0119] In one embodiment of the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-type secondary battery, and particularly, the secondary battery may be a pouch-type secondary battery.

[0120] The present invention will be described in detail below with reference to specific examples. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0121] Example 1 An upper pouch and a lower pouch, each having polyethylene terephthalate / aluminum foil / polypropylene resin laminated in this order, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, each having a positive electrode / separator / negative electrode laminated in this order, was placed inside.

[0122] A vent member was then manufactured by coating both sides of a film of linear low-density polyethylene having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (ExxonMobil, Exceed® 1018, melting point: 119°C, comonomer content relative to the total resin content: 7.6 wt%, weight average molecular weight: 289,053 g / mol, polydispersity index: 3.023, crystallization temperature: 106°C) with a pressure-sensitive adhesive (PSA) (LG Chem, Barrier Pressure-Sensitive Adhesives (BPSA)) to a thickness of 5 μm.

[0123] The vent member thus manufactured was inserted between the polypropylene resins and then heat-sealed to manufacture a secondary battery.

[0124] <Example 2> A secondary battery was manufactured in the same manner as in Example 1, except that a linear low-density polyethylene having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (LG Chem, Lucene®, SP311, melting point: 119°C, comonomer content relative to the total resin content: 9.0 wt%, weight average molecular weight: 270,756 g / mol, polydispersity index: 2.674, crystallization temperature: 107°C) was used instead of the linear low-density polyethylene having a comonomer having 6 carbon atoms used in Example 1.

[0125] Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that a linear low-density polyethylene having a comonomer having eight carbon atoms polymerized in the presence of a metallocene catalyst (Dow Chemical, Elite (registered trademark), 5401GT, melting point: 120°C, comonomer content relative to the total resin content: 11.8 wt%, weight average molecular weight: 251,521 g / mol, polydispersity index: 3.796, crystallization temperature: 105°C) was used instead of the linear low-density polyethylene having a comonomer having six carbon atoms used in Example 1.

[0126] <Comparative Example 1> An upper pouch and a lower pouch, each having polyethylene terephthalate / aluminum foil / polypropylene resin laminated in this order, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, each having a positive electrode / separator / negative electrode laminated in this order, was placed inside.

[0127] Then, a linear low-density polyethylene (Exceed (registered trademark), 1018, manufactured by ExxonMobil) having a comonomer with 6 carbon atoms polymerized in the presence of a metallocene catalyst was inserted between the polypropylene resins and heat-sealed to produce a secondary battery.

[0128] <Comparative Example 2> An upper pouch and a lower pouch, each having polyethylene terephthalate / aluminum foil / polypropylene resin laminated in this order, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, each having a positive electrode / separator / negative electrode laminated in this order, was placed inside.

[0129] Then, a vent member was manufactured by coating both sides of a film of linear low-density polyethylene having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (ExxonMobil, Exceed® 1018, melting point: 119°C, comonomer content relative to the total resin content: 7.6 wt%, weight average molecular weight: 289,053 g / mol, polydispersity index: 3.023, crystallization temperature: 106°C) with a pressure-sensitive adhesive (PSA) (LG Chem, BPSA) to a thickness of 20 μm.

[0130] The vent member thus manufactured was inserted between the polypropylene resins and then heat-sealed to manufacture a secondary battery.

[0131] <Evaluation Example 1: Measurement of sealing strength of secondary battery> For the secondary batteries manufactured in Example 1, Comparative Example 1, and Comparative Example 2, the maximum sealing strength between the sealing portion and the vent member at room temperature was measured and is shown in Table 1 below.

[0132] The maximum sealing strength was measured by cutting the case where the vent member was inserted into a piece 15 mm wide and 5 cm long, opening both ends 180° and fixing them to a UTM jig, and conducting a tensile test at 25°C at a speed of 5 mm / min. The maximum value at which the case broke was measured.

[0133] [Table 1]

[0134] From Table 1, it can be seen that the maximum sealing strength at room temperature between the vent member and the sealing part of the secondary battery of Comparative Example 2, in which the thickness of the second layer exceeds 5 μm, is much lower than the maximum sealing strength at room temperature between the sealing part and the vent member of the secondary battery manufactured in Example 1, in which the thickness of the second layer is 5 μm or less.

[0135] <Evaluation Example 2: Measurement of positional deviation of vent components> The positional deviation of the vent member manufactured in Example 1 and the vent member manufactured in Comparative Example 1 was measured.

[0136] The misalignment of the vent member was calculated by marking the insertion position of the vent member by drawing lines on the sealant layer and outer layer of the secondary battery, and then attaching the vent members manufactured in Example 1 and Comparative Example 1 to the sealant layer and sealing them. After sealing, the distance at which the vent member deviated from the line drawn on the outer layer was measured and calculated.

[0137] It can be seen that the positional deviation of the vent member in Example 1 was ±0.5 mm, while the positional deviation of the vent member in Comparative Example 1 was ±2 mm. [Explanation of symbols]

[0138] 10 Secondary battery 11 Electrode Lead 12 Electrode assembly 13 cases 13a Storage area 13b Sealing part 14 Lead Film 15 Venting material 15a Level 1 15b Layer 2

Claims

1. A method for manufacturing a secondary battery, preparing a case including a receiving portion for receiving an electrode assembly and a sealing portion including a sealant resin and formed to seal the electrode assembly; preparing a vent member including a first layer including a resin having a melting point lower than that of the sealant resin, and a second layer located on at least one surface of the first layer and including an adhesive material; fixing the vent member via the second layer to a vent area defined in at least a portion of the case; and sealing the electrode assembly by fusing the sealing portion. The method for manufacturing a secondary battery, wherein the second layer has a thickness of 5 μm or less.

2. The method for manufacturing a secondary battery according to claim 1 , wherein the vent area is located in the sealing portion.

3. The method for manufacturing a secondary battery according to claim 2 , wherein the vent member is formed to be longer than the sealing portion, and the vent member is exposed to both the inside and outside of the case.

4. The method for manufacturing a secondary battery according to claim 3 , wherein after the sealing step, the second layer is located on at least one surface of the first layer exposed to the outside of the case.

5. The method for producing a secondary battery according to claim 1 , wherein the resin having a melting point lower than that of the sealant resin contains linear low-density polyethylene having a comonomer having six or more carbon atoms.

6. 6. The method for producing a secondary battery according to claim 5, wherein the resin having a melting point lower than that of the sealant resin contains linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

7. 6. The method for producing a secondary battery according to claim 5, wherein in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms, a content of the comonomer having 6 or more carbon atoms is 15% by weight or less relative to 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

8. The method for producing a secondary battery according to claim 5 , wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a polydispersity index of 4 or less.

9. The method for producing a secondary battery according to claim 5 , wherein the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is 10° C. or less.

10. 10. The method for producing a secondary battery according to claim 9, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a crystallization temperature of 90°C to 115°C.

11. 6. The method for producing a secondary battery according to claim 5, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a weight average molecular weight of 100,000 g / mol to 400,000 g / mol.

12. 2. The method for producing a secondary battery according to claim 1, wherein the resin having a melting point lower than that of the sealant resin has a melting point of 100°C to 130°C.

13. The method for manufacturing a secondary battery according to claim 1 , wherein the adhesive material comprises an acrylic polymer, polyurethane, epoxy resin, silicone, butyl rubber, polyisobutylene, or two or more of these.

14. The electrode assembly has an electrode lead attached thereto, The method for manufacturing a secondary battery according to claim 1 , further comprising the step of arranging a lead film that covers a portion of an outer surface of the electrode lead and is interposed between the electrode lead and the case.

15. The method for manufacturing a secondary battery according to claim 1 , wherein the secondary battery is a pouch-type secondary battery.

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